U.S. Pat. No. 3,909,211 is directed to a coal desulfurization process wherein powdered coal is reacted with a mixture of NO and air. The reaction temperature is 200.degree. F. The reaction products, according to the patent, are FeSO.sub.4, SO.sub.3 or SO.sub.2 and oxygenated organix sulfur compounds. After washing the oxygenated coal with water, it was further washed with 10-20% sodium hydroxide solution. After the caustic soda wash, the coal is again washed with water to remove any caustic absorbed by the coal particles. The coal is then dried.
The process of U.S. Pat. No. 3,909,211 has several disadvantageous factors in that SO.sub.2 and SO.sub.3 are formed during the reaction, thus it is necessary to scrub the SO.sub.2 evolved using, for example, caustic soda and this will necessitate an additional operation. Also, washing the desulfurized coal with caustic soda has some disadvantages: it is difficult to remove from coal particles and the presence of sodium in coal could cause excess corrosion in boilers.
Further, the reaction temperature of the process is relatively high and care must be taken to prevent coal ignition.
Other prior art of interest is: U.S. Pat. No. 3,214,346 which discloses that acids may be employed to extract or wash coke after it has been reacted with a gaseous oxidizing agent;
U.S. Pat. No. 3,960,513, which discloses that coal may by desulfurized by suspending it in an aqueous medium and subjecting it to oxidation with oxygen at elevated temperatures;
U.S. Pat. No. 3,393,978, which relates to the desulfurization of particulate carbonaceous material in a fluidized bed with steam and an alkaline material. The patent also discloses the utilization of an acid to wash the thus treated material;
U.S. Pat. No. 2,814,588 discloses that coke may be desulfurized, utilizing such materials such as nitrogen, carbon dioxide, carbon monoxide, mathane, ethylene, water gas, anhydrous ammonia and hydrogen;
Similarly, U.S. Pat. No. 2,726,148 discloses that nitrogen, carbon monoxide, carbon dioxide, ammonia, water gas and hydrogen have been utilized to desulfurize coal; and
U.S. Pat. No. 3,148,397 discloses a fluidized bed operation for desulfurizing coal.